The department telephones are a University resource, and fall under the Electronic Communications Policy, allowing for incidental use. However, long distance toll calls for personal business do not fall under incidental use, and the University should be reimbursed by employees for personal calls.
In this situation, there are a couple of options. One, you could remind the employees of their need to reimburse the university for their personal calls and encourage the staff to use a personal cell phone, or a long distance calling card if they need to continue making these types of calls. In addition, if the personal long distance calls continue, you could work with Communications Services to block out-going long distance calls from those phones.
If they continue to choose not to reimburse the university, then the amount needed to cover the costs could be considered compensation and reported on their W-2 at the end of the year.
Productivity should also be a concern if the employees are spending work time on the phone. Employees should utilize their break time or their lunch period for personal calls.